coscast head(c20let)

[STEVEBOXER]

Hi,did the c20let have a coscast head???????????

[bigdrifter]

Re: coscast head(c20let)

Some did, some didn't - just as hit and miss as XE's

[BazW]

Re: coscast head(c20let)

no, the late ones did but it was a different one to the early Coscasts that were fitted to first GTE16v's

there's a guide in the member section with all the details in

[BazW]

Re: coscast head(c20let)

http://www.astra-mk2.com/forum/showthread.php?t=396&highlight=coscast

[STEVEBOXER]

Re: coscast head(c20let)

Hi baz, mine came out of a n reg calibra turbo.
Do you think it was coscast

[BazW]

Re: coscast head(c20let)

easiest way to spot a Coscast is this...



...U shaped mounts for the heat shield. All Coscasts had these, both early and late. have a look through the guide I posted up, Darren H did it and everything is in there

[STEVEBOXER]

Re: coscast head(c20let)

ok will do,cheers

[gtejon]

Re: coscast head(c20let)

are the heads for the let and xe interchangeable? i have an let about to rebuilt for my champ with a gm head on it, can i replace it with my coscast that came from an f plate gte xe. i appreciate the valves might be different but are the heads themselves the same???

[Mr-G]

Re: coscast head(c20let)

Same head mate just different cams , when you rebuild the LET head use the inlet cam from the XE head though as it has more lift

[gtejon]

Re: coscast head(c20let)

Same head mate just different cams , when you rebuild the LET head use the inlet cam from the XE head though as it has more lift

ahhh so the valves and guides are the same too? that makes life a bit easier!!! so keep the let exhaust cam in and fit an xe inlet cam? i've heard this a lot, why just the inlet cam????

[Mr-G]

Re: coscast head(c20let)

Exhaust cam is specifically designed for turbo applications but the inlet cam is a little lazy, the XE inlet cam has a higher lift an iirc a longer duration so increases tourque.

iirc the later heads had different valve guides and shallower valve seats but other then that they are the pretty much the same. The earlier Coscast heads benefited from hand finished ports whereas the later GM heads were just straight from the cast.

[_SBD16v]

Re: coscast head(c20let)

Exhaust cam is specifically designed for turbo applications but the inlet cam is a little lazy, the XE inlet cam has a higher lift an iirc a longer duration so increases tourque.

both the inlet and exhaust are specifically designed for turbo on the c20let

just like the inlet an exhaust are specifically designed for n/a on the 20xe

the reason a xe inlet is only used is because of the dizzy and hall sensor, if you change for a inlet and exhuast you would need to change the timing of both cams to get rid of some valve overlap something that n/a engines use to ''suck'' in the new charge of air and fuel, however on a turbo engine you can blow the new charge out of the exhuast so we need to get rid of some of the overlap.

now the problem with adjusting both cams is the dizzy on the turbo engine, if you spin around the cam into a different possition you also change the possision of the rotor arm inside the dizzy this changes the ignition timing either retarding it and loosing you power and gaining heat, or advancing it and maybe causing det and a dead engine.

most of us on aftermarkt managment change both

[Frisco]

Re: coscast head(c20let)

So if using standard management with both XE inlet and exhaust fitted would you see more gains than if just the XE inlet was fitted?

Thats if the dizzy was adjusted so that it sits in same plase as it would in standard form ie moved round so the rotor is where it should be (i realise its not as easy as just turning it)

[Mr-G]

Re: coscast head(c20let)

Sorry what i meant was a lot of people KEEP the standard C20LET exhaust cam, but change the inlet cam for the 20XE inlet cam as it has more lift and a longer duration.

[richie00boy]

Re: coscast head(c20let)

Keep the valves from the Coscast in the Coscast as they are different to later ones. Just leave the Coscast all built up and change the exhaust cam for the LET one and fit a vernier on the inlet cam.